1. Field of the Invention
The invention relates to a method for determining a characteristic value for the perfusion of modified tissue regions in organs of living beings.
The invention also relates to a device for determining a characteristic value for the perfusion of modified tissue regions in organs of living beings.
2. Related Prior Art
In dermatology, it is known to use various examination methods, for example direct-light surface microscopy, epiluminescence microscopy, dermatoscopy etc. in order to examine pigmented tissue regions. These examination methods are based on the discovery that the morphology of different tissue regions, especially the microcirculation inside pigmented tissue regions, can be characterised by characteristic values which can be used as evaluation criteria for this tissue region. In this context, it is known that the capillary vessels are pathologically modified in malignant tumors and so-called hypervascularization is formed in the edge region of the tumorous tissue, with capillary blood vessels growing in the direction of the tumor. This phenomenon is referred to as neoangiogenesis (“in-grown vessels”).
It is known to use laser Doppler flowmeters to examine the perfusion in human skin tissue (Kvernmo H. D. et al., Microvascular Research 57, pp. 298–309, 1999). In this context, it is also known to process laser Doppler perfusion signals, which are recorded as a volumetric flow rate as a function of time, specifically by means of a so-called wavelet analysis. The term “wavelet analysis” is intended to mean a method in which a time-variant signal is three-dimensionally represented, specifically over the axes of frequency or scaling, time and signal amplitude. Wavelet analysis is preferably used for those time-variant signals in which a plurality of periodic or quasi-periodic processes are superimposed, possibly together with other stochastic processes. In such a case, wavelet analysis makes it possible to deliberately filter out or deliberately suppress particular frequency or scaling ranges in which individual periodic or quasi-periodic signals occur.
The three-dimensional representation of a laser Doppler perfusion signal by means of wavelet analysis will be referred to below as a “vasomotion field”.
In the article by Kvernmo et al. mentioned above, the perfusion in human skin tissue is examined as a function of the administering of particular vasodilating drugs. The characteristic values determined in the scope of that work therefore relate exclusively to the effect of administering these medicaments. Characteristic values which relate to the perfusion behavior of the tissue itself, particularly in comparison between pigmented and nonpigmented tissue regions, are not disclosed in that paper.